Cells of the reticuloendothelial system are responsible for the removal and digestion of parasitized erythrocytes in malaria. Although the phagocytic cells of the RES are important in the initial processing of particulate antigen prior to antibody synthesis, to what degree this occurs in malaria is unknown. The proposed research is directed toward the utilization of naturally digested parasite components and/or the cells containing this material for specific immunological studies. The naturally digested material from rats infected with malaria (Plasmodium vinckei) may either be extracted from cells of the host's reticuloendothelial system or obtained by culture of such cells in vitro. Spleen macrophages containing parasites, parasitized red cells, cell debris, etc. in all stages of digestion may be cultured for varying lengths of time. Since incubation and extensive washing of cell cultures will insure the absence of infective parasitized red cells, these spleen macrophages may then be used to test their capacity to induce protection against malaria in syngeneic hosts. In addition, parasite material extracted from them may also be used to test for protective capacities. Several alternative methods for digesting parasitized red cells are available. These include the in vitro phagocytosis of infected red cells by explanted spleen or peritoneal macrophages. Similarly, peritoneal macrophages containing parasitized red cells which had been injected intraperitoneally may be explanted and the digestion of the intracellular material allowed to occur in vitro.